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Five months has passed since Islamic State militants were defeated in a bloody and bitter urban siege of Marawi, which left more than 1100 dead and swathes of the city reduced to rubble.

At the time, Australian prime minister Malcolm Turnbull voiced concern Marawi could become the Raqqa of Southeast Asia, referring to Islamic State's reign of terror in Syria.

In the clean-up and rebuilding of Marawi, there appears to be well-founded fears that extremist fighters, carrying large amounts of cash and weaponry, escaped and are regrouping.

The Philippines Army has recently reported jihadist activities in Pantar, Piagapo, Masiu and Pagayawan – all towns close to Marawi in the island of Mindanao.

The southern city of Marawi (marked) in the Philippines was under-siege from Islamic State-linked Maute terrorists for nearly five months. (Google Maps) ()

"Islamic State are operating active cells and sleeper cells in these other outposts," Dupont said.

"Already there has been a spread of the infection from Marawi to other parts of the Philippines."

There are currently 80 Australian special forces personnel deployed in the southern Philippines, a Department of Defence spokesperson confirmed to nine.com.au, training the local army in urban combat and counter-terror tactics.

Australia's Navy has also conducted recent training exercises with their Philippines counterparts to boost maritime security on high-risk boat routes from northern Indonesia and Malaysia.

"We need to work collectively. The Philippines can't handle this on its own," Dupont, a former Australian government security adviser, said.

Philippines leader Rodrigo Duterte has declared a state of martial law on the island of Mindanao through to December 31, in an effort to stop further insurgencies.

President Duterte understands the Philippines needs foreign help to fight Islamic State but he is wary of how such moves are perceived domestically, Dupont said.

A general view of battle damaged Marawi City in the Southern Philippines on October 17, 2017 (GETTY) ()

Along with Australian commandos, US special forces are reportedly training local counterparts inside the Philippines.

"There are political sensitivities ... Duterte doesn't want to be seen to be beholden to other countries because he can't provide security himself," Dupont said.

Leaders from the 10-member ASEAN block arrived in Sydney last weekend, where plans to bolster counter-terrorism cooperation was discussed.

Dupont said the Marawi insurgency had caught the entire region by surprise, but the way ASEAN member countries had quickly cooperated with intelligence and other measures was "encouraging".

Members of the Philippine Marines 1st Brigade conduct a clearing operation in Marawi City, Philippines on September 15, 2017 (GETTY) ()

"The problem in the southern Philippines is probably going to get worse before it gets better," Dupont predicted.

"Over the next two years we are going to see further deterioration of the security situation.

"I think over the medium to long term if we get our settings right and really cooperate effectively it is going to be difficult [for Islamic State] to establish their caliphate in an enduring way. But we are a long way from that point yet."

Maritime tensions in The South China Sea and North Korea's nuclear weapons testing program were also headline grabbing agendas at the weekend's ASEAN special summit of leaders.